Adjustable controllable inductor apparatus



Jan. 3, 1961 P. H. LEE

ADJusTABAE coNTRoLLABLE INDUcToR APPARATUS 2 Sheets-Sheet 1 Filed May 2, 1957 LVRAQM .1.2

INVENTOR. PAUL H. I EE oson TTORNEYS CNY NNW@ 5 Jan. 3, 1961 P. H. LEE 2,967,281

ADJUSTABLE coNTRoLLABLE INDUcToR APPARATUS Filed May 2, 195? 2 sheets-sheet 2 e4 e4 49 49 640 64a ATTORNEYS 2,9572@ Patented Jar?.o 3, i961 ADJUSTABLE CONTROLLABLE IJIJJCTR APPARATUS Paul H. Lee, Norwalk, Conn., assignor to QGS. Laboratories, Inc., Stamford, iConti., a corporation of Connecticut Filed May 2, 1957,Ser.`No 655,559

11-Claimsu (Cl. 33o- 134) 'This invention relates `to adjustable controllable iniductor apparatus and more particularly to apparatus Vfor the adjustment of the reluctance of one or more paths associated with the control Viiux of the controllable inductor. In this way there is provided adjustment of the effective inductance of one or more signal windings each with respect to any given values of the control iiux. The `present invention is particularly well suited for controllable inductor apparatus of the multiple signal winding type `for adjusting the respective etiective inductance values of the various signal windings as functions of the control current to produce the desired relationships between the effective inductance values. For example, the present invention is well suited for controllable inductor apparatus utilized to tune superheterodyne radio receivers for producing the desired "tracking of the various circuits associated with the signal windings yas they are tuned throughout the frequency bands ofthe receivers.

As used herein, the term controllable inductor refers to apparatus including one or more electrical windings, conventionally called the signal windings, each coupled to a signal core portion. The signal core portion includes magnetically saturable material so that changes in the degree of magneticsaturation of the materialfalters the eitective inductance of the signal winding or windings. In use, the signal winding usually is connected into a circuit to be controlled, such as a resonant circuit. The degree of magnetic saturation of the core material associated with the signal winding usually is controlled by changing the current iiow through a control winding electromagnetically coupled to a ilux path which extends through the core portion associated with the signal winding, thereby to control the effective inductance of the signal winding. As the control current is increased, the magnetic saturation of the signal core portionincreases, reducing the permeability of the core material associated with the signal winding and thereby reducing the eiective inductance of the winding. When the control current is reduced the eective inductance of the signal winding increases.

In controllable inductors of the foregoing type, it is advantageous to have means for adjusting the eilfective inductance of the signal windings at any given value of control tiux. For one thing, it is difficult to reproduce the core structures with such precision that each will be aitected in exactly the same manner by any given values of control flux. This is particularly signicant in certain applications of multi-element inductors, where a plurality of signal windings are controlled by common control winding means. When. the signal windings are connected to various tuned circuits in an integrated apparatus wherein the operations of these various circuits are related, it is important that the effective inductance values of l,the various signal windings provide the desired relationships over the range of operation. For example, it often is desirable to tune lelectrical apparatus by providing a plurality of circuits having corresponding frequency response curves which are adjusted in corresponding fashion or in unison so that the frequency response characteristics of the circuits follow along together or track each other.

ln a copeuding application of Ellery P. Snyder, Serial No. 637,505, led January 3l, 1957, now Patent No; 2,911,529, and assigned to the same assignee as the present application, there is described and claimed improved controllable inductor apparatus providing one or more adjustable non-magnetic gaps in the magnetic iiux path or paths associated with a controllable inductor, whereby to provide adjustment of the effective inductance of the signal windings at any given values of the control tlux. The present invention enables precise accurate adjustment of the etective inductance values of controllable inductors of the foregoing type to provide the desired relationship to the control current.

ln accordance with one aspect of the illustrative embodiment of the present invention described herein two control flux kpaths `acting in parallel extend into each signal core portion. One of these control iiux paths remains iixed and the reluctance of the other is adjustable as desired to adjust theeffective inductance value of the signal winding with respect to the control current.

In accordance with another aspect of the illustrative embodiment of thepresent invention the signal core portions of the controllable inductor remain fixed in position withrespect to the control core structure and auxiliary or supplemental pole members provide adjustment of the reluctance between the pontrol core structure and the .signal core. portions. The" supplemental pole members provide a second adjustable iiux path acting in parallel with a ixed flux path between the control core structure and the signal core portions. Fixed nonmagnetic spacers or shimsare positioned in the fixed ux path thereby to limit the proportionate amount of kthe control flux therein, thus enhancing the erectof the second adjustableux path.

Advantageously, the supplemental pole member provides adjustment of the control sensitivity. Among the many further advantages of the illustrative embodiment of this invention are those resulting from the tact that when an adjustment ismade to increase the control sensitivity, the supplemental pole members increase their effective area closely adjacent to the control core structure while at the same time increasing their eliective area adjacent to the signal core portion.

A more complete analysis of the present invention and its various features and advantages will be found in the following description of an illustrative embodiment thereof, which is to be read in conjunction with the accompanying drawings, in which:

Figure l is aperspective view, shown on an enlarged scale and partially broken away, of a controllable inductor embodying the invention;

Figure 2 is a separate perspective viewkof one or" the fixed circular pole pieces of the controllable inductor of Figure l;

Figure 3 is an exploded perspective view of one of the signal winding assemblies in the controllable inductor of Figure l;

Figure 4 is a diagrammatic Aplan view of one of the signal windings and its core, showing the flux paths associated therewith;

Figures 5 and 6 are partial sectional views of opposite end portions, respectively, of one of the signal Winding assemblies of the controllable inductor of Figure l, showing the relation thereof to the gap adjustment means and the pole pieces;

Figure 7 illustrates aplan View of a sheet material blank whichkis bent yup into form suitable for holding ends of the signal kwinding core portions with respect to the fixed pole pieces; and

Figure 8 is a view of a spring clip for holding the other ends of the signal winding core portions.

The multi-element controllable inductor shown in Figure 1 comprises three separate signal winding assemblies 10, 11 and 12 symmetrically disposed within a control winding 14. This arrangement of components within the control winding and control core s-tructure has the advantage of being substantially immune to inliuences of stray fiux elds from any origin. The control winding 14 is wound on a bobbin 15 which is large enough to accommodate the three signal winding assemblies 11i-12 inside of itself.

The signal winding assemblies 19-12 extend between evenly spaced portions of a pair of fixed circular magnetizable end plates or pole pieces 16 and 17 which are disposed at opposite ends of the control winding and bobbin structure 14, 15. Advantageously, these end plates or pole pieces 16 and 17 are formed of soft iron or similar magnetizable material and serve both as core elements for carrying the magnetic control flux circuit as well as providing support means for the signal winding assemblies 1t), 11, and 12. These two end plates are identical, and are held in place at opposite ends of the bobbin by means of spring clips or inwardly bent tabs 1S.

These pole plates 16 and 17 have three rectangular tabs or support platforms 19 (please also see Figure 2) which are struck o-ut of the plates at uniformly spaced positions 120il apart and extend inwardly toward each other within the bobbin 15. Opposed pairs of these tabs are aligned in coplanar relation to serve as mounting support platforms for the signal winding assemblies 10, 11, and 12.

With this arrangement, it can be seen that the three signal winding assemblies 11t-12 in effect form a threesection core for the control winding 14. They provide three parallel and substantially identical control linx paths between the pole pieces 16 and 17 for carrying control fiux generated by the ow of current through the winding 14.

As shown in detail in Figures l and 3, each of the signal winding assemblies 10, 11 or 12 comprises a core 22 in the form of a pair of elongated square bars 23 of saturable magnetic material, for example, such as ferromagnetic ceramic material, often called ferrite, placed longitudinally adjacent to one another. The ferrite material may be similar to that disclosed by Snoek in U.S. Patents Nos. 2,452,529; 2,452,530; and 2,452,531.

A generally elongated hexagonal opening 24 in ythe core 22 is formed by trapezodal recesses in the adjoining sides of the two bars 23. A signal winding 26 is associated with the core 22 and is formed in two halves, each extending through the signal winding opening 24 and connected in series so that their magnetic fields are in aiding relationship around the opening 24 to induce a flow of fiux around the opening as shown schematically by the arrows 25-1 in Figure 4. The control ux, on the other hand, in flowing through the core structure 22, will follow parallel paths extending substantially the full length of the core 22 as indicated by the arrows .Z5- 2, so that the control and signal flux fields are not mutually coupled. The signal fiux is alternating in direction, while the control flux may be a generally unidirectional flux whose value is varied only as necessary to regulate the degree of magnetic saturation of the core 22 and particularly the saturation of the edges of the core adjacent the hole 24 on which the two sections of the winding 26 are wound.

The permeability of the ferrule material in the core 22 decreases rather strikingly with an increase in the degree of its magnetic saturation produced by the control flux 25-2. Thus, the inductances in the signal circuits of each of the windings 26 are changed in accordance with the magnitude of the control current in the control Windlng 14. Since the three signal winding assembles 1042 are bridged across between the pole pieces 16, 17 and suhq i jected to substantially equal amounts of control flux for any given amount of control current, the effective inductance values of the three signal windings change correspondingly as the control current is changed. That is, their effective inductance values tend to track along together or in unison.

As explained in said copending application of Snyder, provision is made for convenient individual adjustment of the effective inductance of each signal winding at any given value of the control ux, whereby each winding can be adjusted precisely to the same or to predetermined different inductance values as desired. For this purpose, adjustable non-magnetic gaps 27 are provided in series with the fiux paths 25-1 of the signal windings. As shown in Figure 4, this non-magnetic gap 27 is an air gap between the ends of the core pieces 23 formed by spreading them slightly apart. The separation 27 is exaggerated in Figure 4 for purposes of emphasis.

The effects of varying these non-magnetic gaps in the inductor flux paths is analyzed in the following manner:

In general, the inductance L of a signal winding S4 can be represented by the expression:

nz (1) L-- where n is the total number of turns of the signal winding 26 and R is the total reluctance of the magnetic circuit 25-1 traversed by the signal tiux induced by current iowing in this winding. Also,

where Rf is the reluctance of the core structure associated with the winding and Rt.,r is the reluctance of any air gap in the co-re structure, that is, of any gap 27 in series with the magnetic circuit 25-1.

Accordingly, the eective signal winding inductance Leif can be expressed as Neglecting fringe effects, the reluctance of an air gap is directly proportional to the width A of the gap measured in a direction parallel to the direction of the iux passing across the gap and inversely proportional to the cross sectional area A of the gap as measured perpendicular to the ux. This is expressed:

where K is a constant of proportionality.

Then, when the gap 27 is reduced to zero, the only reluctance present is that of the ferrite core material, and so the inductance with no gap is expressed as:

Solving for Rf in terms of L0, this becomes:

Substituting for R, and Rg in equation (3), it becomes:

n2 1 Leif-.-ay-A LU'l A L., A where C is a constant equal to K/ n2.

In other words, the effective inductance of each signal winding 25 is a function of the effective inductance of the same winding with no gap, as modified by the eflect oi the gap, and this effect is such as to decrease the effectivz.- inductance as the gap A is increased and vice versa.

The apparatus for adjusting this gap 27 is described and claimed in said copending Snyder application and will be described in connection with this illustrative apparatus further below.

i j asomar In this type of controllable inductor another adjustable air gap is provided' for each of the signal winding assemblies 1042'. This is possible because each of these signal windings 26 is electromagnetically influenced by the two ux paths 25--1 and 25-2, as previously pointed out in connection with the discussion of Figure 4. This other adjustable gap is in series with the main control flux path 25-2 which extends through the signal Winding core pieces from end to end thereof.

In the illustrative embodiment of the present invention, the path of the main contro-l flux is effectively provided with an adjustable gap 28 (please also see Figure in series with the control iiux path 25-2 through each of the signal winding assemblies by means of aA movable supplementary or auxiliary pole piece 29 of highly permeable material. This movable supplemental pole piece 29 advantageously makes possible the adjustment of the air gap 28 without moving the signal winding core 22 in any way with respect to the lixed pole tab 19.

At one end, the ferrite core pieces 23 are held between the projecting arms Sil of a spring clip 32- (please see Figure l). This spring clip 32 is bent up from a T-shaped sheet (Figure 7) ot non-magnetic resilient material, such as brass or beryllium copper. The botto-m arm of this T-shaped piece is bent up along two parallel folds 3dand 36 to form a first U-shaped socket 33 (please see Figure 3) adapted to embrace and firmly grip onto the adjacent support tab 19. The two side arms 3i) are bent toward each other alo-ng pairs of parallel folds di) and 42 so as to form side closures for the socket 38. Then the ends of the arms 3@ are bent out into parallel relationship to define a second socket for gripping the end of the core 22 and for pressing the two core pieces 23 firmly against each other. A finger 46 is bent out and forms an end abutment for this second socket rmly folding the ends of the core pieces properly aligned. It will be appreciated that the areaV 50 of the socket 38 forms a non-magnetic shim between the core 22 and the adjacent support tab 19.

The end plate 16 underlies a circular plate S2 of insulating material which has three slots 53 formed therein adjacent to the support tabs 19 and aligned with that edge of the tab opening 5d which is opposite to the tab 19.

One leg 29 of the adjustable l.-shaped supplementary pole member S6 of magnetizable material extends through the slot 53 generally parallel to the tab 19 andl spaced therefrom, so as to be positioned near to the end portion of the core 22 (please see Figure 5). One leg 57 of an L-shaped spring 58 of non-magnetic material urges the supplementary pole leg 29 away from the core 22. This spring leg 57 normally forms an obtuse angle with its other spring leg 59, as illustrated in Figure 3 whereas the legs 29 and 6i) of the L-shaped magnetizable pole member are substantially at right angles to each other. The end of the spring leg 59 is folded around the end of the corresponding leg 6@ of the supplementary pole member S6, and they are adjustably fastened to the top of the co-rresponding leg 6@ of the supplementary pole member 56, and they are adjustably fastened to the top of the upper plates 52 and 16 by means of an adjusting screw 61. Accordingly, the spring leg 57 presses against the flat face of the core structure 22 and exerts a force tending to raise the upper leg 6h and thereby urges the supplementary pole leg 29 away from the core structure. By tightening the screw 61, the pole leg 29 is forced toward the core portion 22. It will be appreciated that both legs of the supplemental pole member 56 are active in reducing the reluctance between the pole 16 and the signal core portion 22. As the area of the leg 29 moves closer to core 22, the area of leg 60 moves closer to pole 16. Thus, a compound adjustment action is obtained wherein the effectiveness of two areas of the supplemental pole member 56 simultaneously increase to reduce the reluctance to passage ofthe control iiux from the pole 16 through the member 56 to the core portion 22.

It will be appreciated that there are two magnetic circuit paths acting in parallel from the pole piece 16 into the signal core portion 22. One path extends from the support tab 19 thro-ugh the shim area Si) into the end of the core 22. The other is through the supplementary pole member 29 and across the air gap 23 into the core 22. It is the path through this latter member 29 which provides the adjustable gap eiectively in series with the co-ntro-l flux path.

The eiect of varying the gap 2S is analyzed as follows: When this gap is large, it presents a high reluctance, so that the only effective way for the control liux to pass into the core 22 is by means of the pole tab 19. For any given value of control current, the proportionate amount of control flux iiowing along the path 25--2 through the signal core 22 is smaller. This proportionate reduction in control ux becomes increasingly greater as the control current is increased, tending to saturate the tab 19. Thus, when the gap 255 is increased, the rate of change of inductance for a given change in control current is reduced, i.e. a reduction in control sensitivity is obtained which also means a smaller range of inductance change for a given change in control current, and this sensitivity reduction is more marked at higher values of control current. When the gap 28 is reduced, the control sensitivity for the signal winding is increased, giving a greater range of inductance change for a given range of control current change.

The presence of the non-magnetic shim iti advantageously enhances the eiiechveness of the gap adjustment 2S by limiting the proportionate amount of control nur; which can enter the core portion 22 from the tab 19.

This, then, enables convenient adjustment of an air` gap in the control winding magnetic circuit through the signal core 22 so as to give an inductance adjustment predomLnating at the high control iiux density end, Le., at the high control current end of the control current. curve, and yet the signal core advantageously remains fixedl inposition with respect to the pole tab 19.

The apparatus for adjusting the gaps 27 for controlling the i-nductance of the signal windings, as claimed in said Snyder application, is at the opposite end of the signal core portions 22 from the clips 32. The opposite end of each signal core portion 22 is supported from one of the tabs 19 by a spring clip 62. This clip has a pair of opposed co-operating arms 63 which are generally tri-shaped as seen axially of the core 22 (please see Figure 8). An opposed pair of recesses 64 in these arms define a first socket for embracing the end of the support tab 19. A second socket for holding the end of the signal core 22 and mounting it on the adjacent support tab 19 is defined by a second opposed pair of recesses 6fm. As shown in Figure 8, the arms 63 are formed from a resilient strip of non-magnetic material such as brass or beryllium copper with both ends bent into an E-shape to form the pairs ot recesses 64 and 6de. The projecting lug between the recesses 64- and 64a forms a nonmagnetic spacer or shim 65.

The clips 62 not only engage the ends of the signal core pieces so as to hold them in position, but they also have a supplementary U-shaped spring portion 66 which provides a spring force tending to separate the two adjacent ends of the core pieces 23. As best seen in Figures 6 and 8, the opposed ends of the U-portion 66 have laterally projecting teeth 67 (Figure 8) that extend into slots 6?, (Figure 4) near the ends of the core pieces 23, exerting ra separating force thereon. These core pieces 23 are resiliently restrained by a resilient ring 7d, but are normally maintained somewhat separated by the action of the U-portion 66 (as shown somewhat exaggerated in Figure 4).

As shown most clearly in Figures 3 and 6, the U-portion 66 may be formed by a bight in the strip which is bent to form the clip.

To adjust the gap spacing thus provided between the ends of the core pieces 23, a llat rigid strip of non-magnetic material bent into an L-shaped control lever has one leg '72 adjustably fastened to the adjacent end plates 52 and 17 by an adjusting screw '73. The inner leg 74 of the lever extends through the opening 54- left by striking out the tab 19 and through a slit 75 in an insulation plate 52a and lies in a plane generally perpendicular to the outer leg 72. This inner leg 74 lies adjacent to the side face of one of the core pieces 23 and its end is bent over as seen in Figures 3 and 6, so as to press against the end of the adjacent core piece 23. Upon tightening the adjusting screw 73, this core piece is forced toward the other core piece by the lever leg 7d, thereby reducing the gap 27 between the two core pieces. This provides inductance adjustment for the signal winding structure which predominates at the low control current end, i.e., low control ux end of the control curve because the unity permeability of the air gap 27 is then in greater contrast to the much higher permeability of the unsaturated core pieces, as previously indicated.

A return path for the control flux between the pole plates le and i7 is provided by a cylindrical shell 32 of magnetically soft permeable material such as transformer iron. The tabs i8 project from opposite ends of this shell and are bent over the insulation disks 52 and 52H to hold the structure together.

ln the assembled inductor, the three signal circuit assembies iti, ll, and l2 preferably are separated from each other by a minimum spacing of about 1/16 inch between the closest parts. Also, they are shielded from each other bv a symmetrical, Y-shaped shield element Sti (Figure 7) of electrically conductive non-magnetic material, such as copper or aluminum. The shield 80 is located at the center of the assembly with its three uniformly spaced branches extending radially outwardly between the three signal winding assemblies. Further shielding from stray electrostatic effects is obtained for the three structures by the wires in the control winding i4.

In a typical inductor of the type shown in Figures 1-6, the control winding was formed of 25,000 turns of #40 wire. The signal windings were formed of lOO turns of #35 wire. The core pieces 23 were approximately ll/s inches long, and 1/s inch square in cross section. The elongated signal opening 24 was 1/s of an inch wide and BA; of an inch long from end to end, the full width of this opening extending for 1A of an inch, with the ends converging at the taper of 45.

From the foregoing, it will be understood that the embodiment of the present invention described above is well suited to provide the advantages set forth, and since changes may be made in this embodiment of the invention and as the controllable inductor apparatus described herein may be varied in various parts, all without departing from the scope of the invention, it is to be understood that all matter hereinbefore set forth or shown in the accompanying drawings is to be interpreted as illustrative, the scope of the present invention being dened bv the following claims in view of the prior art.

l claim:

l. A controllable inductor including multiple signal windings and means for adjusting the control action thereof comprising a control core structure of magnetically permeable material including two spaced pole portions, control winding rneans mounted on said core structure, a plurality of signal winding cores each including saturable magnetic material extending between said pole portions, a signal winding wound on each of said cores, a pair of magnetically permeable members adjacent to each of said cores defining a pair of tlux paths extending in parallel relationship from a pole portion of the control core structure into each of said cores, said control winding means being electromagnetically coupled by said pole portion to said pairs of parallel flux paths, one of the members of each pair being movable with respect to the pole portion and a mechanically adjustable element for moving one of the members of each pair for dening an adjustable non-magnetic gap in one of each of said pairs of parallel flux paths for adjusting the reluctances thereof, whereby to adjust the control action of each of said signal windings with respect to said control winding means.

2. An adjustable controllable inductor including a plurality of signal windings, a control winding, a magnetically permeable structure electromagnetically coupled to said control winding including a pole portion of said structure, a plurality of signal winding cores, a signal winding on each of said signal winding cores, a plurality of movable supplementary pole pieces, each pole piece being mounted on a pole portion of said structure adjacent to a respective one of said signal winding cores and each delining a supplementary flux path between said pole portion of the structure and its respective associated signal winding core, and adjustment means co-operable with each of said supplementary pole pieces for adjustably moving said supplementary pole pieces for adjusting the spatial relationship thereof to the associated signal winding cores, whereby to vary the reluctances of said supplementary ux paths.

3. An improved adjustable controllable inductor comprising control winding means a plurality of magnetizable components defining a magnetic ux path for conducting flux originating at said control winding means and comprising a magnetically saturable signal core portion and a pole structure adjacent to said signal core portion, a signal winding electromagnetically coupled to said signal core portion, and a movable magnetizable member adjacent to said magnetizable components and detining a supplementary ilux path between said pole structure and said signal core portion, said magnetizable member being movable to alter the spatial relationship between said member and at least one of said magnetizable components whereby to alter the reluctance of said supplementary flux path.

4. An adjustable controllable inductor including a plurality of signal windings, control winding means, a magnetically permeable structure electromagnetically coupled to said control winding means and defining a plurality of ux paths acting in parallel for conducting magnetic flux created by current tlow through said control winding, said liux paths all having a common portion delined by a pole portion of said structure, a plurality of signal cores of permeable material extending from said pole portion and each dening a portion of one of said parallel ux paths, a plurality of signal windings, one on each of said signal cores, a plurality of L-shaped members of magnetizable material each having one leg adjacent to said pole portion and its other leg adjacent to an end portion of one of said signal cores to provide supplementary magnetic flux paths from said one pole portion to the associated signal cores, spring means engaging each said member and extending between said member and the adjacent signal core and exerting a force urging said other leg away from said end portion of one of said signal cores, and adjusting means engaging each said member for moving said member against the opposite force of said spring means, whereby to vary the reluctance of the flux paths between said signal cores and said pole portion for adjusting the effective inductance values of each of said signal windings.

5. An adjustable controllable inductor including a plurality of signal windings, a control winding, a magnetically permeable structure electromagnetically coupled to said control winding including a pair of flat, circular pole pieces at opposite ends of said control winding, said pole pieces being concentric with said control winding and parallel to each other, a plurality of signal cores of permeable material extending between said pole pieces, a plurality of signal windings each coupled to one of said signal cores, a plurality of movable supplementary pole pieces of magnetizable material extending from one of said circular pole pieces and each lying adjacent to an end portion of one of said signal cores to provide a magnetic iiux path from said one circular pole piece to the end portion of the adjacent signal core, and adjusting means for moving each of said supplementary pole pieces for varying the spacing between said end portion of each said signal core and the adjacent one of said supplementary pole pieces whereby to vary the reluctance of the flux paths between said signal cores and said one circular pole piece for adjusting individually the inductance values of said signal windings.

6. A controllable inductor including means for adjusting the control sensitivity comprising a control winding, a magnetically permeable pole structure associated with said control winding, a signal core portion including magnetically saturable material, a signal winding coupled to said signal core portion whose inductance is controlled by the degree of saturation of said saturable material, means securing said signal core portion in iixed relationship with respect to said pole structure, a iirst iixed permeable member on said pole structure defining a first iixed liux path passing from said pole Structure to said signal core portion, a second member of permeable material at least partially extending between said signal core portion and said pole structure and defining a second ux path passing from said pole structure to said signal core portion, at least a part of said second member being movable, and adjustment means for moving said part for adjusting the reluctance of said second path, whereby to adjust the control sensitivity between said control winding and said signal winding.

7. A controllable inductor as claimed in claim and wherein a non-magnetic spacer is positioned between said pole structure and said signal core portion for limiting the amount of iiux in said iirst iinx path.

8. An adjustable controllable inductor including a control winding, a magnetically permeable core structure which is electromagnetically coupled to said control winding, signal core means including magnetically saturable material, a signal winding electromagnetically coupled to said signal core means, a plurality of magnetically permeable components defining a pair of liux paths in magnetically parallel relationship intermediate said core structure and said signal core means for conducting magnetic flux from said control winding into said signal core means, and manually adjustable means associated with one of said pair of flux paths for varying the reluctance of said one ux path.

9. A controllable inductor including a control structure of magnetically permeable material having two pole portions, a control winding on said structure, a plurality of elongated elements of magnetically saturable material extending between said pole portions, a plurality of signal windings adapted to have alternating current signals applied thereto, said signal windings being mounted on respective ones of said saturable elements, and an adjustment mechanism for manually adjusting the inductance of one of said signal windings with respect to another comprising a magnetically permeable member movably mounted upon one of said pole portions closely adjacent to one of said saturable elements and an adjusting screw for moving said member toward and away from the adjacent element.

l0. A controllable inductor as claimed in claim 9 and wherein said magnetically permeable member includes two areas, said adjusting screw moving one of said areas into more eiiective flux coupled relationship with said adjacent element and simultaneously moving the other of said areas into more effective ux coupled relationship with said pole portion upon which it is mounted.

11. A controllable inductor as claimed in claim 10 and wherein said member is L-shaped and is effectively hinged near the corner thereof, said adjusting screw moving one arm of the L-shaped member closer to said adjacent member while moving the other arm of the L- shaped member closer to the pole portion.

References Cited in the le of this patent UNITED STATES PATENTS 2,158,613 Loughlin May 16, 1939 2,241,912 Kersten et al. May 13, 1941 2,488,393 Geiselman Nov. 15, 1949 2,683,820 Sherman July 13, 1954 

